The present invention relates to bone fixation systems and, more particularly, deployment devices and absorbable or nonabsorbable bone fixation pins of the type for fixing soft tissue or tendons to bone or for securing two or more adjacent bone fragments or bones together.
Bones which have been fractured, either by accident or severed by surgical procedure, must be kept together for lengthy periods of time in order to permit the recalcification and bonding of the severed parts. Accordingly, adjoining parts of a severed or fractured bone are typically clamped together or attached to one another by means of a pin or a screw driven through the rejoined parts. Movement of the pertinent part of the body may then be kept at a minimum, such as by application of a cast, brace, splint, or other conventional technique, in order to promote healing and avoid mechanical stresses that may cause the bone parts to separate during bodily activity.
The surgical procedure of attaching two or more parts of a bone with a pin-like device requires an incision into the tissue surrounding the bone and the drilling of a hole through the bone parts to be joined. Due to the significant variation in bone size, configuration, and load requirements, a wide variety of bone fixation devices have been developed in the prior art. In general, the current standard of care relies upon a variety of metal wires, screws, and clamps to stabilize the bone fragments during the healing process. Following a sufficient bone healing period of time, the percutaneous access site or other site may require re-opening to permit removal of the bone fixation device.
Long bone fractures are among the most common encountered in the human skeleton. Many of these fractures and those of small bones and small bone fragments must be treated by internal and external fixation methods in order to achieve good anatomical position, early mobilization, and early and complete rehabilitation of the injured patient.
The internal fixation techniques commonly followed today frequently rely upon the use of Kirschner wires (K-wires), intramedullary pins, wiring, plates, screws, and combinations of the foregoing. The particular device or combination of devices is selected to achieve the best anatomic and functional condition of the traumatized bone with the simplest operative procedure and with a minimal use of foreign-implanted stabilizing material. A variety of alternate bone fixation devices are also known in the art, such as, for example, those disclosed in U.S. Pat. No. 4,688,561 to Reese, U.S. Pat. No. 4,790,304 to Rosenberg, and U.S. Pat. No. 5,370,646 to Reese, et al.
Notwithstanding the common use of the K-wire to achieve shear-force stabilization of bone fractures, K-wire fixation is attended by certain known risks. For example, a second surgical procedure is required to remove the device after healing is complete. Removal is recommended, because otherwise the bone adjacent to an implant becomes vulnerable to stress shielding as a result of the differences in the modulus of elasticity and density between metal and the bone.
In addition, an implanted K-wire may provide a site for a variety of complications ranging from pin-tract infections to abscesses, resistant osteomyelitis, septic arthritis, and infected nonunion.
Another potential complication involving the use of K-wires is in vivo migration. Axial migration of K-wires has been reported to range from 0 mm to 20 mm, which can both increase the difficulty of pin removal as well as inflict trauma to adjacent tissue.
As conventionally utilized for bone injuries of the hand and foot, K-wires project through the skin. In addition to the undesirable appearance, percutaneously extending K-wires can be disrupted or cause damage to adjacent structures such as tendons if the K-wire comes into contact with external objects.
Notwithstanding the variety of bone fasteners that have been developed in the prior art, there remains a need for a bone fastener of the type that can accomplish shear-force stabilization with minimal trauma to the surrounding tissue both during installation and following bone healing.
In addition, there remains a need for a simple, adjustable bone fixation device which may be utilized to secure soft tissue or tendon to bone.
There is provided in accordance with one aspect of the present invention, a fixation pin for fixing bone to bone or other tissue to bone. The fixation pin comprises a body, having a proximal end and a distal end. A distal anchor is on the body. The distal anchor comprises at least a first retention surface on a first axially extending lever arm and a second retention surface on a second axially extending lever arm. Preferably, the first and second retention surfaces are laterally moveable between a first, implantation crossing profile and a second, larger, deployed crossing profile. The first and second retention structures are preferably biased in the direction of the second crossing profile. In certain embodiments, at least three retention surfaces and at least three lever arms are provided. The fixation pin may be integrally formed from a single piece of metal which may comprise titanium.
The fixation pin may further comprise a retention structure on the body, for retaining a proximal anchor. The retention structure may comprise a deviation in the surface of the body, such as an annular ridge, helical thread, or other recess or projection. A proximal anchor is movably carried by the body.
The fixation pin may additionally comprise at least one breakpoint on the body, for allowing a proximal projection of the body to be snapped off, following tensioning of the proximal anchor.
In accordance with another aspect of the present invention, there is provided a fixation pin for bone to bone or other tissue to bone fixation. The fixation pin comprises a tubular body, having a proximal end and a distal end. At least two slots are provided in the tubular body, extending proximally from the distal end to define at least a first and a second axially extending lever arms. A proximally facing retention surface is carried by each lever arm. A retention structure is also provided on the body, for removably carrying a proximal anchor. The first and second retention surfaces are laterally moveable between an implantation crossing profile and a deployed crossing profile.
The retention structure may comprise a thread on the body, proximal to at least a portion of the lever arms. A proximal anchor is movably carried by the thread.
In accordance with another aspect of the present invention, there is provided a method of fixing a first material to bone. The method comprises the steps of providing a pin having a distal anchor and at least one proximal breakpoint. The distal anchor is advanced through the first material and into the bone. A proximal anchor is advanced distally along the pin to secure the first material to the bone. Lateral pressure is applied to a proximal portion of the pin, to break the pin at the breakpoint.
In one application of the method, the first material comprises bone. In alternate applications, the first material comprises soft tissue, tendon, graft or other synthetic or natural biological material.
In one application, the advancing the distal anchor step comprises advancing the distal anchor all the way through the bone. The advancing a proximal anchor step may comprise rotating the proximal anchor with respect to the pin.
The method may further comprise the step of removing the proximal anchor by rotating the proximal anchor with respect to the pin. A core drill may thereafter be advanced over the pin, and the pin removed from the bone.
In accordance with another aspect of the present invention, there is provided a fixation pin for fixing a first material to bone. The pin comprises an elongate tubular body, having a proximal end and a distal end. A plurality of deflectable barbs are carried by the distal end. A thread is provided on the tubular body, in-between the proximal end and the distal end, and a break point is provided on the tubular body, proximal to at least a portion of the thread.
The pin may further comprise a proximal anchor, removably retained on the tubular body by the thread. A rotational coupling is provided on the pin, for coupling to a tool. A second rotational coupling is provided on the anchor, to permit rotation of the anchor while resisting rotation of the pin. Each of the barbs may be attached to the tubular body by an axially extending lever arm.
Further features and advantages of the present invention will become apparent to those of skill in the art in view of the detailed description of preferred embodiments which follows, when considered together with the attached claims and drawings.